1. Field of the Invention
The present invention relates to a tracking error detecting method, a tracking error detecting apparatus and an optical recording and reproducing apparatus for use in optically recording and reproducing information on and from an optical recording medium, such as an optical disc and an optical card.
2. Description of the Related Art
In recent years, various types of optical recording mediums with different recording densities have been developed. For example, a CD (Compact Disc) of which available wavelength of laser light is near 780 nm, for example, a DVD (Digital Versatile Disc) of which available wavelength of laser light is near 660 nm, a BD (Blu-ray Disc: Trademark) of which available wavelength of laser light is near 405 nm, and HD-DVD (High Definition DVD) of which available wavelength of laser light is near 405 nm might be enumerated as disc-like optical recording mediums.
These optical recording media are respectively different in structure. In order to increase recording density, a track pitch of 1.6 μm of a CD type optical recording medium is miniaturized as 0.74 μm in the DVD type optical recording medium, and it is also microminiaturized as approximately 0.3 to 0.35 μm in the BD-type optical recording medium.
With respect to the recording track of which track width is microminiaturized as described above, it is necessary to locate light emitted from a light source at target recording tracks with high accuracy.
A DPP (Differential Push-Pull) method is widely used as a method for correcting the offset of an objective lens, that is, the shift of an optical axis of the objective lens in a tracking method using a push-pull signal (see Cited Patent Reference 1, for example).
According to this DPP method, light traveling from the light source to the optical recording medium is divided into three lights, two sub-beams are irradiated on the position shifted by ½ of the track pitch of the recording track with high accuracy in the radial direction on the surface of the optical recording medium relative to the middle main beam, and the tracking error can be detected and the offset of the objective lens can be canceled by detecting these lights at the light-receiving units.
[Cited Patent Reference 1]: Japanese Examined Patent Publication No. H04-34212